The invention relates to inclination measurement apparatus and more particularly to inclination measurement apparatus capable of inclination measurements with an accuracy in the order of 10xe2x88x924xc2x0.
In U.S. Pat. No. 5,210,954 to Schafler, there is illustrated and described an inclination measurement apparatus designed to compensate for a clinometer""s inherent susceptibility to bias and gain changes for issuing accurate inclination measurements of the inclination of a surface with respect to X and/or Y measurement axes. The inclination measurement apparatus includes a clinometer mounted on a turntable vertically displaceable with respect to a base plate by way means of a lifting device whereby, pursuant to an initial upward displacement of the turntable away from the base plate, a half-turn rotation, and a final downward displacement theretoward, the clinometer is indexable between a pair of precisely reproducible diametrically opposite orientations with respect to a desired measurement axis for bias correction. The turntable is also tiltable in the direction of two diametrically opposed calibration axis for gain correction. Moreover, a clinometer is only truly accurate at rest and also requires a relatively long settling down time after being displaced during a bias correction procedure before being truly accurate again, thereby resulting in a relatively lengthy xe2x80x9cdead timexe2x80x9d during which time the inclination measurement apparatus is effectively inoperable. More problematic though is that even a slight change in inclination, or worse still a sudden jolt, or the like, during a bias correction procedure yields a presumed accurate bias value which is, in fact, inaccurate leading to inaccurate inclination measurements until the next unaffected bias correction procedure.
Generally speaking, an inclination measurement apparatus in accordance with the present invention includes an indexable clinometer bearing turntable rotatable in a single plane between a pair of precisely reproducible diametrically opposite orientations with respect to a desired measurement axis for respectively issuing inclination measurements V0 and V180 responsive to the inclination of a surface with respect to the desired measurement axis. The inclination measurement apparatus also preferably includes a reference clinometer for enabling uninterrupted accurate bias corrected inclination measurements of the inclination of the surface with respect to the desired measurement axis by virtue of its inclination measurements being employed for calculating bias corrected inclination measurements at least during periodic bias correction procedures depending on the mode of operation of the inclination measurement apparatus, and monitoring their validity. The reference clinometer is also preferably selectively disposable between a pair of gain calibration positions subtending a predetermined highly accurate angle therebetween in a plane perpendicular to the desired measurement axis, thereby enabling its gain to be periodically determined for improving the accuracy of its inclination measurements.
The inclination measurement apparatus of the present invention can be implemented as either a single axis inclination measurement apparatus or a dual axis inclination measurement apparatus. A single axis inclination measurement apparatus typically includes a pair of co-aligned single axis clinometers, for example, the TS30 model commercially available from Singer Instruments and Control Ltd, Tirat Carmel, Israel. Based on the principle of the single axis inclination measurement apparatus, a dual axis inclination measurement apparatus includes a reference dual axis clinometer or, alternatively, a pair of mutually perpendicular reference single axis clinometers. Also, an indexable dual axis clinometer or, alternatively, a pair of mutually perpendicular indexable single axis clinometers or, alternatively, a single indexable single axis clinometer rotatable between two mutually perpendicular pairs of precisely reproducible diametrically opposite orientations. It should be noted that there are no absolute constraints regarding the relative orientations between the reference clinometer(s) and the indexable clinometer(s) of a dual axis inclination measurement apparatus but they are preferably co-aligned to simplify calculating bias corrected inclination measurements with respect to desired mutually perpendicular measurement axes.